Process of deoiling slack wax



F 1942- R. K. STRATFORDV 2, ,1

PROCESS OF DEO ILING SLACK WAX Filed Jan. 11, 1939 WA x y (if) C'H/LLER 2 .zswaxma 6 f I sol-VENT :7 F/L T ER fiWAXfiD SLACK WAX FIL TER Patented Feb. 17, '1942 urrs STATS AENT OFFICE PROCESS or DEOILING SLACK wax Application January 11, 1939, Serial No. 250,305

.(Cl. 19e 20 3 Claims.

The present invention relates to the refining of petroleum waxes. The invention is particularly directed to a method of de-oiling wax cakes produced by solvent dewaxing processes By the process of the present invention the last traces of oil are removed from the wax cakes by subjecting the cake to compression at temperatures substantially above the dewaxing temperature.

Various processes are known in the art by which waxy petroleum distillates are dewaxed and the separated waxy constituents refined. For example, it is known to chill waxy lubricating oil distillates to temperatures at which the waxy constituents precipitate. The precipitated waxy constituents are separated from the chilled mixture by sedimentation, filtering and the like. The separated wax cake known as slack wax is usually subjected to so-called sweating operations in which the temperature of the wax cake is gradually raised causing the oil to seep and flow in order to remove entrained oil. These sweating operations, however, are not entirely satisfactory for the reason that it is practically impossible to remove the last traces of oil from the wax without incurring an undue wax loss. Furthermore in sweating operations the relatively low melting point waxes are invariably removed with the oil. Thus, in order to reduce wax losses and to produce waxes of low oil content, various modifications of the above-described process are employed. In order to efiiciently handle viscous oils by the press method, it is also known to use so-called solvent dewaxing processes.

In solvent dewaxing operations a suitable solvent, as for example, a solvent selected from the class of liquefied normally gaseous hydrocarbons, ketones, acetone, benzol and the like, is employed. In these processes the solvent is usually added to the oil and the oil and solvent chilled to a dewaxing temperature either by direct or indirect means. If the solvent employed is propane or a similar solvent, it is the customary practice to allow suflicient solvent to evaporate in the chiller to cool the mixture to the desired dewaxing temperature. The waxy constituents are removed from the dewaxed oil by filtering, decantation, or by other suitable means. In certain processes, it is the custom to wash the wax cake with a suitable washing solvent, such as naphtha, in order to reduce the amount of oil in the wax cake. These processes, however, have not been satisfactory for economically producing substantially oil-free wax without the necessity of a subsequent sweating stage.

I have now discovered a process which will materially reduce the amount of oil in the wax cake and by which it is possible to dispense entirely with the sweating operation. In accordance with my invention the slack wax cake is mixed volume of waxy distillate.

with additional solvent, repuddled and repressed at a temperature above the initial filtering temperature. My dewaxing process produces a wax cake which contains less oil than is usually secured by normal sweating operations. The process of my invention may be readily understood by reference tothe attached drawing showing one modification of the same.

A waxy lubricating oil distillate is introduced into chiller 2 by means of feed line I. Prior to introduction into chiller 2 the lubricating oil distillate is diluted with a suitable solvent introduced into line I by means of line 3. If desirable, the diluted waxy distillate may be heated to a temperature at which complete miscibility occurs between the waxy constituents, the diluent and oil by means of heating equipment t. In chiller 2 the diluted waxy distillate is cooled either by direct or indirect means to a suitable dewaxing temperature. For example, if liquefied propane is employed as a diluent, sufiicient prop'ane may be allowed to evaporate in chiller 2 to secure the desired chilling. The vaporized sol vent is removed from chiller 2 by means of line 5. The chilled mixture is removed by means of line 6 and the dewaxed oil separated from the slack wax in filter press I. The dewaxed oil is removed by means of line 8 and the slack wax by means of line 9. The slack wax is then rendered fluid or puddled by mechanical agitation in agitator ll. Additional solvent may be introduced by means of line Ill. The mixture is removed from agitator H by means of line l2 and introduced into filter I3 where it is filtered and compressed. The wax cake after being filtered in filter [3 may be washed with a washing solution introduced by means of line I5 before being compressed. After compression the substantially oil-free wax cake is removed by means of line IS.

The process of the present invention may be widely varied. Any suitable dewaxing solvent may be utilized, as for example, liquefied normally gaseous hydrocarbons, ketones and the like. The quantity of dewaxing solvent used will depend upon the particular waxy distillate being dewaxed and the dewaxing solvent or solvent mixture used. In general, it is preferred to use from 1 to 3 volumes of dewaxing solvent per For example, when using methyl normal butyl ketone as the dewaxing solvent, it ispreferred to use from 1 /2 to 2 volumes of methyl normal butyl ketone per volume of waxy distillate. The waxy distillate and dewaxing solvent are preferably heated to a temperature at which complete miscibility occurs between the oil, the waxy constituents and the dewaxing solvent. When using methyl normal butyl ketone, the mixture is heated in the rang from F. to F.

The heated mixture is chilled to a temperature at which the waxy constituents precipitate. The rate of chilling from the miscibility temperature to the dewaxing temperature is preferably adjusted to secure maximum capacity of the equipment and to secure desirable wax crystalline structure in order to facilitate subsequent filtering. In general, it is preferred to chill rather rapidly through an initial chilling stage, to chill at a relatively slow rate through an intermediate chilling stage and to rapidly chill through the final chilling stage. Usually the mixture is chilled to a dewaxing temperature in the range from F. to +25 F. The precipitated waxy constituents may be separated from the dewaxed oil and solvent by any suitable means, as for example, by sedimentation, filtering, centrifuging and the like. In general, it is preferred to recover the slack Wax from the dewaxed oil and solvent by means of filters.

The slack wax secured in this manner is rendered fluid by mechanical means, refiltered and subsequently compressed at relatively high temperatures in order to secure a relatively oil-free wax. The particular sequence of steps employed may vary and will depend to a large extent upon the characteristics of the slack wax being deoiled. For example, when the slack wax contains less than 6% to 8% of oil, based on solvent-free slack wax, desirable results are secured by puddling the slack wax cake without additional solvent, followed by filtering the puddled cake and subsequently compressing the same. This operation may be conducted at any desirable temperature, although it is best conducted at a temperature in the range of 30 F. to 60 F., preferably in the range from 40 F. to 50 F. The pressure used is 10 lbs. to 40 lbs. per square inch, preferably a pressure of 25 lbs. to 35 lbs. per square inch.

When the slack wax cake contains more than 6% to 8% of oil, based on solvent-free slack wax, it is preferred to modify the above-described procedure. Desirable results are secured by puddling the slack wax cake with the addition of from one to, two volumes of solvent per volume of slack wax cake. The puddled mixture is filtered and compressed under the conditions as described above.

Slack Wax cakes containing more than about 6% to 8% of oil may be puddled without the addition of solvent, filtered and compressed as described provided the filtered wax is washed with fresh solvent prior to or during compression. It has been found that especially desirable results are secured by washing the wax cake during compression. I have also discovered that under certain conditions it is desirable to substitute a centrifugal compression step for the filtration and compression stages.

The process may be applied in the removal of oil from wax cakes containing a relatively large amount of the same. For example, it may be desirable to subject the Wax cakes to several pressing operations at progressively higher temperatures and pressures. The operation, however, is particularly applicable to wax cakes secured from solvent dewaxing operations and gives desirable results when the wax cake is secured from a hot and cold pressing operation. The temperatures employed will, of course, depend upon the melting point desired in the final wax product, as well as upon the characteristics of the wax being treated. The pressures employed will likewise depend upon these factors, as well as upon the temperature employed. In general,

it is preferred to subject the wax cake to a pressure of 10 lbs. to 40 lbs. per square inch at a temperature in the range from 30 F. to 60 F.

In order to further illustrate the invention, the following examples are given which should not be construed as limiting the invention in any manner whatsoever:

EXAMPLE 1 A Mid-Continent waxy lubricating oil distillate was diluted with 3 volumes of methyl n-butyl ketone. The mixture was heated to a temperature of about 120 F. and then chilled to a temperature of 14 F. The dewaxed oil was separated from the waxy cake and the cake was washed with approximately .69 volumes of methyl nbutyl ketone per volume of Wax cake. The slack Wax cake was separated and had the following analysis:

F. and subjected to a pressure of about 18 lbs. per square inch. The composition of the wax cake after this treatment and the composition of the filtrate removed were as follows:

TABLE 2 Wax cake Filtrate Volumes Volumes Wax l6. 7 Wax 1. 8 Oil 0.7 Oil 2. 3 Solvent 18. 6 Solvent 60. 0

From the above data it may be readily seen that approximately of the wax was recovered in the wax cake and that approximately 77% of the oil was removed.

The ratio of oil to solvent was approximately constant throughout the experiment. By further compressing the cake at higher pressure more complete de-oiling is to be expected.

EXAMPLE 2 A Mid-Continent intermediate distillate having a viscosity of '74 seconds Saybolt Universal at 210 F. was dewaxed at 13 F. when using methyl normal butyl ketone as the dewaxing solvent. The wax cakes were puddled and filtered and compressed.

TABLE 3 De-oilz'ng waa: cakes from solvent dewazm'ng M id- Continent intermediate distillate Composition of the original wax cake Cake 1 Cake 2 Wax .per cent. 19. 4 13. 4 Oil d0 5.2 0.8 Methyl'normal butyl keton do 75. 4 85. 8 Oil in wax scale 21. l 5. 6

7 TABLE 3-Continued De-oiZz'n-g results, compressing at about +30 F.

Wax Fil- Wax Fil- 5 cake trate cake trate 7 51. 3 29. 2 71. 8 0. 3 13. 6 04 2 3. 3 0. 2 5 47. 7 l5. 4 63. 4 More ax to be recycle l. 5 2. Oil in wax scale (by analysis do 10 4 1 Expressible oil contentdo 0 Wax cakes were washed underthe following conditions:

TABLE 6 De-oiling operating data gggg Washed Washed Temperature F +2? +3 -5. 3 t. 1 41.. 1 52. 2 41. 1 29. 2

The analysis of the de-oiled wax cake from these operations is summarized below:

From the above data it may be readily seen that the oil content of the wax cake having an oil content of 1.5 is lower than the oil content of waxes produced by commercial sweating operations. It also should be noted thatthe lower the oil content of the original wax cake, the greater is the degree of de-oiling obtained.

EXAMPLE 3 Cake 1 of Example 2 was de-oiled in the manner described, using temperatures of 15 F., F. and 43 F. in the compression stage. The results secured by these operations are summarized below:

From the above data it is to be noted that substantial reduction of oil in the wax cake was secured.

EXAMPLE 4 Wax cakes of the following composition were washed before the compression step for de-oiling of the wax:

TABLE 5 Efiect of washing prior to compression on the deoiling of wax Composition of the wax cake (charge Not to e omng) washed Washed Washed Wax per cent. 19. 4 19.4 20. 3 Oil d0 5.2 5.2 1.4 Solvent (methyl normal butyl ketone) per cent 75. 4 75.4 78. 3 Oil in wax scale do 21. 1 21. 1 6. 5 Oil-solvent ratio--- 6. 9 6. 9 l. 8 Wax/solvent ratio. 25. 8 25. 8 25. 9 Liquids/solids ratio 4. 15 4. 15 3. 93

From the above data it is apparent that when the oil in the slack wax is relatively high, as for example, in the range of about 21%, Washing of the wax cake will materially reduce the oil in the final wax product. Although the oil in the wax cake is reduced from 21.1% to 8.1% when not Washed, when washing in accordance with the present invention, the oil in the wax cake was reduced from 21.1% to 1.2%. The data furtherillustrate that when the oil in the wax cake is in the range below about 6% to 8%, substantially oil-free wax is secured without the necessity of washing.

EXAMPLE 5 A slack wax cake having the following composition was puddled with and Without additional solvent. After puddling, the cake was filtered and compressed at a temperature of about 43 F. to 46 F.

TABLE 8 Effect of diluting the was: cake prior to de-ozlz'ng Composition of the wax cake (charge to de-oiling):

The wax cakes secured by these operations were as follows:

TABLE 10 Wax Fil- Wax Fil- Wax Fil- Recovery cake trate cake trate cake trate 40.1 59.9 40.5 159.5 41.7 258.3 18. l 1. 8 16. 7 2. 7 15. 3 4.0 1. 6 3. 7 7 4. 5 5 4. 8 Solvent do- 20. 4 54. 4 23. 1. 152. 3 25. 9 249. 5 Oil in wax cake (by analysis 8. 1 4. 0 3. 1 Expressible oil 2. 5 8

From the above data it may be readily seen that greater de-oiling is secured from wax cakes having a relatively high oil content by Puddling with additional solvent, followed by filtering and compressing at elevated temperatures.

EXAMPLE 6 A wax cake having the following composition was repuddled and centrifuged. This was com- I claim:

1. Process of de-oiling slack wax containing more than about 8% of oil, comprising puddling and filtering said wax, followed by washing with a dewaxing solvent and then compressing the wax cake at a pressure of from about 10 lbs. to 40 lbs. per square inch at a temperature in the range from 30 F. to 60 F.

2. Process as defined by claim 1, in which the pared with filtering and compressing the cake 1Q pressure is at least 25 pounds per square inch after repuddling. The results of these operations are summarized as follows:

and in which the temperature is at least 40 F. 3. Process as defined by claim 1, in which the TABLE 11 Wax cake Solution stream Gentri- Gentrif- Proccssemploycd Temp. Pres. fuging ugal 011 W time force inwax ax rc- Yield Scale Yield O11 rec y cycled F. LbsJsq. in. Minutes LbsJlb. Parts Percent Parts Percent Percent I 440 I 44. 9 10.9 50. 9 62. 16. centrifuging 35. 6 i. 7 58. 7 77. 8 l5. 7 35. 3 8. 9 55.0 68. 5 8.0 Filtration and compression. :3; 3:: t;

Centrifugal force F=0.000341 Wr (R. P. M.) where W is weight of particle in pounds, 1 is radius of curvature of path in feet, and R permits. 35

. P. M. is angular velocity in revolutions per minute.

wax is puddled with from one to two volumes of a dewaxing solvent and in which the wax cake 30 is compressed at a pressure of at least 25 pounds per square inch and at a temperature of at least 40 F.

REGINALD K. STRATFORD 

